在熊猫间隔上进行操作

Question

r = [[0,2],[2,4],[4,6],[6,8]]
i = [pd.Interval(x[0],x[1]) for x in r]
df = pd.DataFrame({"x":["a","b","a","b"],"i":i})

我正在尝试对具有间隔数据的列执行操作

df["sum"] = df.apply(lambda x: sum(x.i),axis=1)

但是我得到一个错误

TypeError: ("'pandas._libs.interval.Interval' object is not iterable", u'occurred at index 0')